Fuel-based injection control

ABSTRACT

Systems and methods of operating an engine with a varying fuel composition. In one example, a split injection is performed during engine cranking with at least some fuel injected in the intake stroke and some fuel injected in the compression stroke. Further, a split ratio of the injection is adjusted based on the alcohol content of the injected fuel.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 12/885,208, filed on Sep. 17, 2010, now U.S. Pat. No.8,447,496, the entire contents of which is incorporated herein byreference for all purposes.

FIELD

The present application relates to methods and systems for controlling afuel injection of an internal combustion engine operating with fuel ofvarying composition.

BACKGROUND AND SUMMARY

Alternate fuels have been developed to mitigate the rising prices ofconventional fuels and for reducing production of regulated emissions,such as CO₂. For example, alcohol and alcohol-based fuel blends havebeen recognized as attractive alternative fuels, in particular forautomotive applications. Various engine systems may be used with alcoholfuels, utilizing various engine technologies such as turbo-chargers,super-chargers, etc. Further, various approaches may be used to controlsuch alcohol-fuelled engines, including adjustment of boost or sparktiming in dependence upon an alcohol content of the engine fuel, andvarious other engine operating conditions.

One example approach to control alcohol-fuelled engines is described byBrehob in U.S. Pat. No. 7,287,509. Herein, the injection timing of adirectly injected alcohol fuel is adjusted to take advantage of theincreased charge cooling effects of the alcohol fuel's higher heat ofvaporization and increased octane. Specifically, the injection timing ofone or more direct injections is advanced with increased alcohol in thefuel to take advantage of the higher latent enthalpy of vaporization ofalcohol and to allow more time for vaporization. Further, in someembodiments involving multiple injections, a larger amount of fuel isinjected in an earlier injection (such as in an intake stroke) while asmaller amount of fuel is injected in a later injection (such as in acompression stroke or exhaust stroke). By advancing the injectiontiming, and/or injecting a larger fraction of fuel in an earlierinjection, the intake system is cooled to enable the charge density thatcan be rammed into the combustion chamber to be increased. Overall, thecharge cooling effect of the alcohol fuel is used to improve the peaktorque output of the engine.

However, the inventors herein have recognized potential issues with suchan approach. In one example, during an engine cold-start, when thetemperature conditions of the engine are already not hot enough for anefficient combustion, advancing the injection timing responsive to anincrease in fuel alcohol content may further cool the system andsignificantly reduce the efficiency of fuel evaporation and theformation of a homogeneous air-fuel mixture. Injecting a larger fractionof fuel in an earlier injection may further degrade fuel evaporationefficiency. The larger amount of time required to evaporate the fuel maydegrade engine startability. Additionally, the charge cooling effect ofthe alcohol fuel on the intake system may further lower the air-chargetemperature at cold-start conditions thereby further degradingcombustion stability and increasing potential for engine misfire. Assuch, this may lead to reduced fuel economy and degraded cold-startexhaust emissions.

Thus in one example, some of the above issues may be addressed by amethod of operating an engine cylinder including a direct fuel injector.In one embodiment, the method comprises, during an engine cold start,direct injecting at least some fuel in an intake stroke of the engineand at least some fuel in a compression stroke of the engine, anddecreasing a ratio of intake stroke fuel to compression stroke fuel asan alcohol content of the injected fuel increases.

In one example, the engine may be a flex-fuel engine of a vehicleconfigured with direct fuel injection. During an engine cold-start, whenoperating the engine with an alcohol-blended fuel, such as during afirst number of combustion events from the start of engine rotation, asplit fuel injection may be performed with at least some fuel injectedin the intake stroke of the cylinder and at least some fuel injected inthe compression stroke of the cylinder. The split ratio of theinjections, for example, a ratio between an amount of fuel injected inthe first intake stroke and an amount of fuel injected in the secondcompression stroke, may be adjusted based on the alcohol content of theinjected fuel. As such, the split ratio may have a value between 0and 1. Herein, the ratio of intake stroke fuel to compression strokefuel may be decreased as the alcohol content of the fuel increases.While the split ratio is decreased, the injections may be adjusted sothat a start of injection timing in the intake stroke and an end ofinjection timing in the compression stroke is maintained, even as thealcohol content of the fuel changes, the split ratio changes, and thetotal amount of fuel injection changes.

The number of combustion events, at engine cranking, over which thesplit injection with the decreasing split ratio is performed may also beadjusted based on the alcohol content of the fuel. Similarly, a numberof engine cylinders for which split fuel injection with the decreasingsplit ratio is performed may also be adjusted based on the alcoholcontent of the fuel. In one example, one or more of the number ofcombustion events since the beginning of engine rotation and the numberof engine cylinders may be increased as the alcohol content of theinjected fuel increases.

In one example, when operating with a fuel-blend with a lower percentageof alcohol (such as E10, which has approximately 10% ethanol and 90%gasoline), the split ratio may be higher, for example, closer to 1, sothat a larger amount of fuel may be injected in the intake stroke whilea smaller amount of fuel is injected in the compression stroke. Inanother example, when operating with a fuel-blend with a higherpercentage of alcohol (such as E70, which has approximately 70% ethanoland 30% gasoline), the split ratio may be lower, for example, closer to0, so that a smaller amount of fuel may be injected in the intake strokewhile a larger amount of fuel is injected in the compression stroke).Further, the number of compression stroke injections may be increased asthe compression stroke injection amount exceeds a threshold.

By performing multiple injections and adjusting the split ratio of themultiple injections based on the alcohol content of the injected fuel,engine combustion, particularly during engine cranking, may be improvedwhile reducing particulate matter emissions. Specifically, by increasingthe proportion of fuel injected in the compression stroke as the alcoholcontent of the fuel increases, the higher air-charge temperature andhigher valve temperature of the engine cylinders during the compressionstroke may be advantageously used to more effectively evaporate thedirectly injected alcohol fuel and form a homogenous air-fuel mixture.In this way, the engine's ability to start with alcohol fuels may beimproved. Additionally, by evaporating most of the injected fuel, lessfuel may be lost during engine operation, and the need for larger orpilot fuel injections at engine cold-start may be reduced or eliminated.As such, this may provide fuel economy benefits as well as reducedcold-start exhaust emissions. Finally, by maintaining the start ofinjection timing of the intake injection and the end of injection timingof the compression injection, it is possible to maintain repeatableengine speed profiles.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example embodiment of a combustion chamber operatingwith a direct fuel injector;

FIG. 2 shows a high level flow chart illustrating a routine that may beimplemented for adjusting the split ratio of a direct fuel injectionresponsive to fuel composition;

FIG. 3 shows a map depicting variations in injection split ratio withfuel alcohol content; and

FIG. 4 shows a fuel injection chart with example variations in injectionsplit ratio for fuels with differing alcohol content.

DETAILED DESCRIPTION

The following description relates to systems and methods for improvingan engine's ability to start with alcohol based fuels (such as theengine of FIG. 1) at ambient temperatures (cold-start). An enginecontroller may be configured to perform a control routine, such asdepicted in FIG. 2, during an engine cold start, to adjust the splitratio of the amount of fuel injected during an intake stroke to anamount injected during a compression stroke of the engine responsive tothe fuel composition, for example, the fuel alcohol content. Bydecreasing the ratio of intake stroke fuel to compression stroke fuel asthe fuel alcohol content increases, as depicted in FIGS. 3-4, fuelevaporation and formation of a homogeneous air-fuel mixture atcold-start may be improved, without the need for pilot fuel injections.By reducing fuel losses incurred during cold-start, the fuel efficiencyand quality of vehicle cold-start exhaust emissions may be significantlyimproved.

FIG. 1 depicts an example embodiment of a combustion chamber or cylinderof internal combustion engine 10. Engine 10 may receive controlparameters from a control system including controller 12 and input froma vehicle operator 130 via an input device 132. In this example, inputdevice 132 includes an accelerator pedal and a pedal position sensor 134for generating a proportional pedal position signal PP. Cylinder (hereinalso “combustion chamber’) 14 of engine 10 may include combustionchamber walls 136 with piston 138 positioned therein. Piston 138 may becoupled to crankshaft 140 so that reciprocating motion of the piston istranslated into rotational motion of the crankshaft. Crankshaft 140 maybe coupled to at least one drive wheel of the passenger vehicle via atransmission system. Further, a starter motor may be coupled tocrankshaft 140 via a flywheel to enable a starting operation of engine10.

Cylinder 14 can receive intake air via a series of intake air passages142, 144, and 146. Intake air passage 146 can communicate with othercylinders of engine 10 in addition to cylinder 14. In some embodiments,one or more of the intake passages may include a boosting device such asa turbocharger or a supercharger. For example, FIG. 1 shows engine 10configured with a turbocharger including a compressor 174 arrangedbetween intake passages 142 and 144, and an exhaust turbine 176 arrangedalong exhaust passage 148. Compressor 174 may be at least partiallypowered by exhaust turbine 176 via a shaft 180 where the boosting deviceis configured as a turbocharger. However, in other examples, such aswhere engine 10 is provided with a supercharger, exhaust turbine 176 maybe optionally omitted, where compressor 174 may be powered by mechanicalinput from a motor or the engine. A throttle 20 including a throttleplate 164 may be provided along an intake passage of the engine forvarying the flow rate and/or pressure of intake air provided to theengine cylinders. For example, throttle 20 may be disposed downstream ofcompressor 174 as shown in FIG. 1, or alternatively may be providedupstream of compressor 174.

Exhaust passage 148 can receive exhaust gases from other cylinders ofengine 10 in addition to cylinder 14. Exhaust gas sensor 128 is showncoupled to exhaust passage 148 upstream of emission control device 178.Sensor 128 may be selected from among various suitable sensors forproviding an indication of exhaust gas air/fuel ratio such as a linearoxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), atwo-state oxygen sensor or EGO (as depicted), a HEGO (heated EGO), aNOx, HC, or CO sensor, for example. Emission control device 178 may be athree way catalyst (TWC), NOx trap, various other emission controldevices, or combinations thereof.

Exhaust temperature may be estimated by one or more temperature sensors(not shown) located in exhaust passage 148. Alternatively, exhausttemperature may be inferred based on engine operating conditions such asspeed, load, air-fuel ratio (AFR), spark retard, etc. Further, exhausttemperature may be computed by one or more exhaust gas sensors 128. Itmay be appreciated that the exhaust gas temperature may alternatively beestimated by any combination of temperature estimation methods listedherein.

Each cylinder of engine 10 may include one or more intake valves and oneor more exhaust valves. For example, cylinder 14 is shown including atleast one intake poppet valve 150 and at least one exhaust poppet valve156 located at an upper region of cylinder 14. In some embodiments, eachcylinder of engine 10, including cylinder 14, may include at least twointake poppet valves and at least two exhaust poppet valves located atan upper region of the cylinder.

Intake valve 150 may be controlled by controller 12 by cam actuation viacam actuation system 151. Similarly, exhaust valve 156 may be controlledby controller 12 via cam actuation system 153. Cam actuation systems 151and 153 may each include one or more cams and may utilize one or more ofcam profile switching (CPS), variable cam timing (VCT), variable valvetiming (VVT) and/or variable valve lift (VVL) systems that may beoperated by controller 12 to vary valve operation. The position ofintake valve 150 and exhaust valve 156 may be determined by valveposition sensors 155 and 157, respectively. In alternative embodiments,the intake and/or exhaust valve may be controlled by electric valveactuation. For example, cylinder 14 may alternatively include an intakevalve controlled via electric valve actuation and an exhaust valvecontrolled via cam actuation including CPS and/or VCT systems. In stillother embodiments, the intake and exhaust valves may be controlled by acommon valve actuator or actuation system, or a variable valve timingactuator or actuation system.

Cylinder 14 can have a compression ratio, which is the ratio of volumeswhen piston 138 is at bottom center to top center. Conventionally, thecompression ratio is in the range of 9:1 to 10:1. However, in someexamples where different fuels are used, the compression ratio may beincreased. This may happen, for example, when higher octane fuels orfuels with higher latent enthalpy of vaporization are used. Thecompression ratio may also be increased if direct injection is used dueto its effect on engine knock.

In some embodiments, each cylinder of engine 10 may include a spark plug192 for initiating combustion. Ignition system 190 can provide anignition spark to combustion chamber 14 via spark plug 192 in responseto spark advance signal SA from controller 12, under select operatingmodes. However, in some embodiments, spark plug 192 may be omitted, suchas where engine 10 may initiate combustion by auto-ignition or byinjection of fuel as may be the case with some diesel engines.

In some embodiments, each cylinder of engine 10 may be configured withone or more fuel injectors for providing fuel thereto. As a non-limitingexample, cylinder 14 is shown including one fuel injector 166. Fuelinjector 166 is shown coupled directly to cylinder 14 for injecting fueldirectly therein in proportion to the pulse width of signal FPW receivedfrom controller 12 via electronic driver 168. In this manner, fuelinjector 166 provides what is known as direct injection (hereafter alsoreferred to as “DI”) of fuel into combustion cylinder 14. While FIG. 1shows injector 166 as a side injector, it may also be located overheadof the piston, such as near the position of spark plug 192. Such aposition may improve mixing and combustion when operating the enginewith an alcohol-based fuel due to the lower volatility of somealcohol-based fuels. Alternatively, the injector may be located overheadand near the intake valve to improve mixing. Fuel may be delivered tofuel injector 166 from a high pressure fuel system 8 including fueltanks, fuel pumps, and a fuel rail. Alternatively, fuel may be deliveredby a single stage fuel pump at lower pressure, in which case the timingof the direct fuel injection may be more limited during the compressionstroke than if a high pressure fuel system is used. Further, while notshown, the fuel tanks may have a pressure transducer providing a signalto controller 12. It will be appreciated that, in an alternateembodiment, injector 166 may be a port injector providing fuel into theintake port upstream of cylinder 14.

It will also be appreciated that while in one embodiment, the engine maybe operated by injecting the variable fuel blend via a single directinjector; in alternate embodiments, the engine may be operated by usingtwo injectors (a direct injector and a port injector) and varying arelative amount of injection from each injector.

Fuel may be delivered by the injector to the cylinder during a singlecycle of the cylinder. Further, the distribution and/or relative amountof fuel delivered from the injector may vary with operating conditions,such as air charge temperature, as described herein below. Furthermore,for a single combustion event, multiple injections of the delivered fuelmay be performed per cycle. The multiple injections may be performedduring the compression stroke, intake stroke, or any appropriatecombination thereof.

As described above, FIG. 1 shows only one cylinder of a multi-cylinderengine. As such each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector(s), spark plug, etc.

Fuel tanks in fuel system 8 may hold fuel with different fuel qualities,such as different fuel compositions. These differences may includedifferent alcohol content, different octane, different heat ofvaporizations, different fuel blends, and/or combinations thereof etc.In one example, fuels with different alcohol contents could include onefuel being gasoline and the other being ethanol or methanol. In anotherexample, the engine may use gasoline as a first substance and an alcoholcontaining fuel blend such as E85 (which is approximately 85% ethanoland 15% gasoline) or M85 (which is approximately 85% methanol and 15%gasoline) as a second substance. Other alcohol containing fuels could bea mixture of alcohol and water, a mixture of alcohol, water andgasoline, a mixture of ethanol, methanol and water, etc. In stillanother example, both fuels may be alcohol blends wherein the first fuelmay be a gasoline alcohol blend with a lower ratio of alcohol than agasoline alcohol blend of a second fuel with a greater ratio of alcohol,such as E10 (which is approximately 10% ethanol) as a first fuel and E85(which is approximately 85% ethanol) as a second fuel. Additionally, thefirst and second fuels may also differ in other fuel qualities such as adifference in temperature, viscosity, octane number, latent enthalpy ofvaporization etc.

Moreover, fuel characteristics of the fuel tank may vary frequently. Inone example, a driver may refill the fuel tank with E85 one day, and E10the next, and E50 the next. The day to day variations in tank refillingcan thus result in frequently varying fuel compositions, therebyaffecting the fuel composition delivered by injector 166.

Controller 12 is shown in FIG. 1 as a microcomputer, includingmicroprocessor unit 106, input/output ports 108, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 110 in this particular example, random access memory 112,keep alive memory 114, and a data bus. Controller 12 may receive varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 122; engine coolant temperature (ECT)from temperature sensor 116 coupled to cooling sleeve 118; a profileignition pickup signal (PIP) from Hall effect sensor 120 (or other type)coupled to crankshaft 140; throttle position (TP) from a throttleposition sensor; and absolute manifold pressure signal (MAP) from sensor124. Engine speed signal, RPM, may be generated by controller 12 fromsignal PIP. Manifold pressure signal MAP from a manifold pressure sensormay be used to provide an indication of vacuum, or pressure, in theintake manifold.

Storage medium read-only memory 110 can be programmed with computerreadable data representing instructions executable by processor 106 forperforming the methods described below as well as other variants thatare anticipated but not specifically listed.

FIG. 2 describes an example control system routine 200 for adjusting asplit ratio of a direct fuel injection responsive to fuel composition.Specifically, based on engine operating conditions, an amount of fuelmay be injected either as a single direct fuel injection a multipledirect fuel injection. In one example, the multiple injections mayinclude injecting at least some fuel in the intake stroke and injectingat least some fuel in the compression stroke. The split ratio of fuelinjected in the compression stroke to the intake stroke may be adjustedbased on fuel composition. By adjusting the split ratio responsive tothe alcohol content of the fuel, the evaporation of the fuel and themixing of the fuel with air may be improved, thereby improving thequality of the combustion event, and an engine's ability to start.

At 202, it may be confirmed whether the engine is in a cold-startcondition. In one example, an engine cold-start may be confirmed if theengine temperature is below a threshold temperature and/or a thresholdduration since a previous engine shutdown has elapsed. If an enginecold-start is not confirmed, the routine may end. Upon confirmation, at204, the engine operating conditions may be measured and/or estimated.These may include an engine speed, an air charge temperature, a manifoldpressure, barometric pressure, etc. At 206, the fuel alcohol contentand/or fuel composition may be determined. In one example, the fuelcomposition may be determined based on a previous engine operation. Inanother example, the fuel composition may be determined based on a fueltank filling event. Alternatively, the fuel composition may bedetermined based on the output of a fuel composition sensor, such as afuel alcohol sensor.

At 208, a fuel injection setting may be determined based on theestimated engine operating conditions, and further based on the fuelcomposition. The fuel injection settings determined may include anamount of fuel to be injected during the combustion event, whether theinjected amount will be injected as a single injection or will be splitbetween multiple injections, as a intake stroke injection or as acompression stroke injection or split between both intake stroke andcompression stroke fuel injections. The injection timing in the event ofa multiple fuel injection may include details regarding the stroke(intake, compression, exhaust, etc.) in which the fuel may be injected,a start of injection timing and an end of injection timing for eachinjection, and a duration of each injection. For example, the start ofinjection timing and/or the end of injection timing may vary with enginespeed, load, or other parameters.

At 210 a split ratio for the fuel injection may be determined based onthe fuel composition. FIG. 3 shows a map 300 depicting an example changein split ratio (along the y-axis) with variation in fuel alcohol content(along the x-axis). Specifically, line 302 depicts a change in the splitratio between a first injection amount and second amount, line 304 showsthe change in the first injection amount, and line 306 depicts thechange in the second injection amount. As such, the split ratio (line302) may have a value ranging between 0 and 1. Thus, a split ratio of 1or 0 may indicate that all the fuel has been injected as a single fuelinjection, while a split ratio between 0 and 1 may indicate that thefuel injection has been split into at least two fuel injections with afirst (earlier) injection and a second (later) injection. Therein, asplit ratio of 1 may indicate that substantially all the fuel has beeninjected in the first, earlier injection while a split ratio of 0 mayindicate that substantially all the fuel has been injected in thesecond, later injection. Similarly, a split ratio value closer to 1indicates that a larger fraction of the injected fuel has been injectedin the first, earlier injection while a split ratio closer to 0indicates that a larger fraction of the injected fuel has been injectedin the second, later injection. In one example, the different splitratios used at the different fuel alcohol contents may be stored in alook-up table in the controller's memory.

In one example, the first injection amount may represent an amount offuel injected in an intake stroke of a cylinder while the secondinjection amount may represent an amount of fuel injected in acompression stroke of the cylinder. As depicted, as the alcohol contentof the injected fuel increases, the split ratio (line 302) may decrease.That is, the first fuel injection amount (line 304), for example, anamount of fuel injected in the intake stroke, may decrease while thesecond injection amount (line 306), for example, an amount of fuelinjected in the compression stroke, may correspondingly increase. Byincreasing the ratio of fuel injected in the second, later injection(for example, in the compression stroke) as the fuel alcohol contentincreases, the injected alcohol may be injected into air charge of ahigher temperature, thereby improving evaporation of the injected fuel.By improving the atomization and mixing of the injected alcohol with theair charge, the engine ability to start may be improved. Furthermore,since substantially all the injected fuel may be evaporated, fuelresiduals may be reduced, thereby improving engine cold-start exhaustemissions.

As such, an amount of fuel injected during the combustion event may bebased on, among other parameters, the intake air charge (amount,temperature, pressure, etc.) which in turn is based on the fuelcomposition (e.g., alcohol content) of the injected fuel. Thus, as thealcohol content of the injected fuel increases, the amount of fuelinjected may also increase. For a fuel of a given alcohol content, thedetermined amount of fuel may be injected as a single injection or splitinto multiple (for example, two) injections. As such, the sum of theamount of fuel injected in the multiple injections will remain the sameas the amount of fuel injected in the single injection. Thus, in oneexample, during an engine cold start, a single fuel injection may beperformed in the intake stroke. In another example, the single fuelinjection of the fuel may be performed in the compression stroke. Instill another example, the amount of fuel injected in the singleinjection may be split into a first injection of a first amount in theintake stroke and a second injection of a second amount in thecompression stroke, wherein the sum of the first and second amount mayequal the amount of fuel injected in the single injection.

The sum of the amount of fuel injected in the intake stroke and thecompression stroke may increase as the alcohol content of the fuelincreases. Further, the split ratio may also be adjusted based on thefuel's alcohol content. As further illustrated with reference to theexample injection settings of FIG. 4, as a fuel alcohol content of theinjected fuel increases, for a given engine speed, a controller may beconfigured to inject a larger proportion of a determined injectionamount in the second, later injection (such as, in the compressionstroke) while injecting a smaller proportion of the determined injectionamount in the first, earlier injection (such as, in the intake stroke).

Returning to FIG. 2, at 212, it may be determined whether any of theinjections are in the compression stroke, and if so, whether thecompression injection amount is greater than an injection threshold. Inone example, the compression injection amount may be greater than amaximum amount that can be dispensed by the injector in a singleinjection. In another example, the compression injection amount may begreater than a threshold amount within engine combustion stabilitylimits. If the compression injection amount is above the threshold, thenat 214, the number of compression injections may be increased and anengine controller may determine that multiple compression injections areto be performed per cylinder and proceed to 216.

In one example, the controller may split the initial compressioninjection amount into a double symmetric compression injection whereinthe amount injected per compression injection may be adjusted to halfthe value of the initial compression injection setting. Additionally,the timing of the two injections may be adjusted such that the averagetiming of the two compression injections is the same as the initialsingle compression injection setting. If required, the duty cycle andfrequency of the fuel injector may also be accordingly adjusted.Specifically, the time of opening and closing of the fuel injector inthe compression stroke may be adjusted (e.g., decreased) and the timingin between the multiple compression injections may be adjusted (e.g.increased) as the number of injections is increased. In this way, byincreasing the number of injections, the determined compressioninjection amount may be injected in multiple installments withoutadversely affecting the engine's performance. If the compressioninjection amount is not above the threshold at 212, and/or after thenumber of compression injections is increased at 214, the routine mayproceed to 216 wherein fuel injection may be performed according to thedetermined settings.

At 218, based on the adjusted split ratio, one or more engine operatingparameters may be adjusted. In one example, ignition spark timing may beadjusted based on the adjusted split ratio. For example, the ignitionspark timing may be retarded as the split ratio is decreased. In anotherexample, fuel rail pressure may be adjusted based on the adjusted splitratio.

In one example, during a first engine cold-start, for example, on afirst day when the fuel tank is filled with a first fuel blend of loweralcohol content, at least some of the first fuel may be direct injectedin the intake stroke of an engine cylinder and at least some of thefirst fuel may be injected in the compression stroke of the enginecylinder at a first split ratio of intake stroke fuel to compressionstoke fuel. In comparison, during a second engine cold-start, forexample, on a second day when the fuel tank is filled with a second fuelthat has a higher alcohol content than the first fuel injected duringthe first engine cold-start, at least some of the second fuel may bedirect injected in the intake stroke of the engine cylinder and at leastsome of the second fuel may be injected in the compression stroke of theengine cylinder at a second, higher split ratio of intake stroke fuel tocompression stoke fuel.

Additionally, the number of combustion events over which the splitinjection is performed may also be adjusted based on the fuel's alcoholcontent. For example, during an engine start at an ambient temperaturewith a first fuel having a lower alcohol content, such as E10 (10%alcohol, 90% gasoline), the number of split direct fuel injection events(that is, the number of combustion events over which the split injectionis performed) may be lower while the split ratio for the fuel injectionevents is higher. In comparison, during an engine start at an ambienttemperature with a second fuel having a higher alcohol content, such asE85 (85% alcohol, 15% gasoline), the number of split direct fuelinjection events (that is, the number of combustion events over whichthe split injection is performed) may be higher while the split ratiofor the fuel injection events is lower. Additionally, or optionally, thenumber of cylinders in which the split injection is performed may beadjusted (e.g., increased) as the fuel alcohol content increases. Forexample, during the first engine cold-start, the direct injection at thefirst (lower) split ratio may be performed in a first number of enginecylinders, while during the second engine cold-start, the directinjection at the second (higher) split ratio may be performed in asecond, higher, number of engine cylinders.

In one example, the engine is a 6 cylinder engine. As one example,during the first engine cold start, direct injection at the first lowersplit ratio may be performed in all engine cylinders for the first twocombustion events. In comparison, during the second engine cold start,direct injection at the second higher split ratio may be performed inall engine cylinders for the first four combustion events. Herein, alarger number of combustion events may be required to raise the cylinderair-charge temperature sufficiently high to enable proper vaporizationof the higher alcohol content fuel. Following the fourth combustionevent, the split injection may be disabled since, by then, each cylindermay have had at least one combustion event and thus the residual heat inthe cylinder may be enough to vaporize the alcohol fuel sufficiently,even at high alcohol amounts.

In another example, during the first engine cold start, direct injectionat the first lower split ratio may be performed in three cylinders ofthe engine for the first three combustion events while during the secondengine cold start, direct injection at the second higher split ratio maybe performed in all (six) engine cylinders for the first six combustionevents. Herein, a larger number of cylinders may require the splitinjection to raise the cylinder air-charge temperature sufficiently highto enable proper vaporization of the higher alcohol content fuel. Stillother combinations of number of cylinders and number of cylinder eventsmay be possible.

Following the predetermined number of combustion events, the split ratiomay be readjusted, for example, the split fuel injection may betransitioned back to a single fuel injection (in the intake stroke only,or in the compression stroke only). During the transition out of thesplit injection, one or more engine operating parameters (e.g., sparktiming, boost, etc.) may be adjusted based on the transition. As oneexample, when an engine is transitioning from a split injection to asingle intake injection, both the spark timing and the throttle may beadjusted. As another example, when an engine is transitioning from splitto compression only injection, only spark timing may be adjusted.

While the above example illustrates performing a split injection duringcranking for a predetermined number of combustion events, it will beappreciated that in an alternate example, the split injection may beinitiated at cranking only after a predetermined number of combustionevents have elapsed. For example, at cranking, a single fuel injection(in the intake stroke only, or in the compression stroke only) may beperformed for a first predetermined number of combustion events, afterwhich, the split fuel injection may be transitioned in and performed fora second different predetermined number of combustion events. In oneexample, split fuel injection may not enable during the first and secondinjection from engine start due to low injection pressure. Split fuelinjection may only be enabled after the first two injections haveelapsed, that is, for the third, fourth, fifth and sixth injection fromthe engine start due to the injection pressure having built up by thethird injection. In one example, at lower ambient temperatures (e.g.,less then 0° C.), following the sixth injection, split fuel injectionmay be disabled since, by then, each cylinder may have had at least onecombustion event and thus the reduced heat loss due to the increasedspeed of the compression and the residual heat in the cylinder may beenough to vaporize the alcohol fuel sufficiently, even at high alcoholamounts. As during the transitioning out, during the transitioning in ofthe split fuel injection, one or more engine operating parameters (e.g.,spark timing, boost, etc.) may be adjusted based on the transition. Inone example, during an engine start at lower ambient temperatures, whentransitioning from a single compression only injection to a splitinjection, both the compression injection timing and the spark timingmay be adjusted.

In this way, the split ratio of fuel injections may be adjustedresponsive to a fuel alcohol content, to improve the evaporation of thefuel during engine cold-start conditions and thus improve the engine'sability to start. Specifically, by increasing the proportion ofcompression injection fuel (and optionally the number of compressioninjections), while decreasing the proportion of intake injection fuel asfuel alcohol content increases, an improved fuel evaporation may beachieved during engine start for fuels with low volatility.

FIG. 4 depicts an example fuel injection timing chart 400 with examplevariations in fuel injection settings, including split ratio (SR), forfuels with differing alcohol content. It will be appreciated that thedepicted examples represent example scenarios wherein engine operatingparameters (such as engine speed, load, etc.) are the same, and whereinthe fuel alcohol content varies. Accordingly, as previously elaboratedwith reference to FIGS. 2-3, the split ratio of fuel injected in a first(earlier) injection to fuel injected in a second (later) injection isadjusted based on the alcohol content of the injected fuel. As such, thesplit ratio may have a value ranging between 0 and 1.

In the first example, the engine is operated with gasoline only. Herein,a single fuel injection may be performed with a split ratio of 1. Asdepicted, all the fuel may be injected as a single injection in theintake stroke (hatched bar). Since gasoline is a high volatility fuel, alower engine temperature may suffice to evaporate the fuel. Thus, anintake stroke injection may enable efficient air-fuel mixing. In thesecond example, the fuel injection of a gasoline fuel is performed withthe split ratio set at 0. Thus, as depicted, all the fuel may beinjected as a single injection in the compression stroke (hatched bar).As indicated by the difference in the width of the hatched bars, due tothe higher cylinder temperature in the compression stroke, a smalleramount of gasoline fuel may need to be injected during the single fuelinjection in the compression stroke (that is, with SR=0) as compared tothe single fuel injection in the intake stroke (that is, with SR=1). Inthe third example, the gasoline fuel injection is split into twoinjections with a split ratio between 0 and 1 (herein, closer to 1 than0) such that a larger portion of the gasoline fuel injection amount isinjected during the intake stroke and the remaining smaller portion ofthe gasoline fuel injection amount is injected during the compressionstroke. In one example, a single fuel injection of gasoline in theintake stroke may be used when the when the engine is a stabilizedoperation temperatures, while the single fuel injection of gasoline inthe compression stroke may be used when the engine is significantlybelow normal operating temperatures. In comparison, the split fuelinjection of the gasoline fuel may be used when it is desirable toretard spark to increase the exhaust temperatures. In still anotherexample, a split ratio of the injections may be gradually transitioned(over a predetermined number of combustion events) from a split ratio of0 to 1, or 1 to 0. As previously elaborated, during a transition of thefuel injection from a single injection (that is, with a split ratio ofeither 0 or 1) to a split injection (that is, with a split ratio between0 and 1), one or more engine operating parameters (such as spark timing,boost, etc.) may be adjusted to compensate for torque disturbances.

In the fourth example, the engine is operated with an ethanol fuel blendof lower alcohol content, such as E10. Herein, a fuel injection (solidbars) may be performed with a split ratio between 0 and 1 (herein,closer to 0 than 1) such that a larger portion of the E10 fuel injectionamount is injected during the intake stroke and the remaining smallerportion of the E10 fuel injection amount is injected during thecompression stroke. As such, a smaller portion of the E10 fuel isinjected during the intake stroke as compared to the portion of gasolinefuel injected during the intake stroke in the preceding example (thatis, the third example illustration a split fuel injection for gasolinefuel). Since ethanol is a low volatility fuel, a higher enginetemperature may be required to evaporate the fuel, particularly at coldambient starts. Thus, at least some of the fuel is injected in thecompression stroke to take advantage of the compression stroke's highercylinder valve temperature and air charge temperature. The fifth, sixth,and seventh examples depict example fuel injections for enginesoperating with fuel having progressively higher fuel alcohol content. Asshown, in each case a split injection may be performed (solid bars) witha split ratio between 0 and 1. Furthermore, as the alcohol content ofthe injected fuel increases (going from E10 to E70), the split ratio maybe gradually decreased such that the intake stroke injection amount isdecreased while the compression stroke injection amount iscorrespondingly increased. By increasing the amount of fuel injected inthe compression stroke, as compared to the intake stroke, fuelatomization and engine's ability to start particularly at cold ambienttemperatures may be improved.

The split ratio of the injections may be adjusted such that a start ofinjection timing of the intake stroke fuel injection amount (as depictedby the left margin of the first solid bar) and an end of injectiontiming of the compression stroke fuel injection amount (as depicted bythe right margin of the second solid bar) is maintained while the splitratio is decreased. As such, one or more of the following start ofinjection timing of the intake stroke, intake fuel injection amount, theend of injection timing for the compression stroke, and the compressionfuel injection amount may be determined based on engine operatingparameters, such as a given engine speed/load condition or desiredspark. However, for a given engine speed/load condition (or other engineoperating parameter), as the alcohol content of the injected fuelchanges and the split ratio is corresponding adjusted, the start ofinjection timing of the intake fuel injection, and the end of injectiontiming for the compression fuel injection is maintained.

It will be appreciated that while the depicted examples show the fuelinjection split between an intake stroke fuel injection and acompression stroke fuel injection, this is not meant in a limitingsense. In alternate embodiments, the split ratio may represent thedistribution of a fuel injection between a first, earlier injection anda second, later injection. For example, in an alternate embodiment, thefirst injection may be in the compression stroke while the secondinjection is in the exhaust stroke. In still other examples, themultiple injections may be in the same stroke.

The eighth example shows an example wherein the engine is operated withan ethanol blend of higher alcohol content, such as E85 to E100. Herein,a single fuel injection may be performed with the split ratio set at 0,that is, with all the fuel injected in the compression stroke. However,if the injection amount exceeds a threshold (such as a threshold amountthat can be dispensed by the injector in a single injection), theinjection amount in the compression stroke may be split into multiplecompression injections. As depicted in the ninth example, when operatingwith E85-E100, a double compression injection may be performed, theamount of the two injections adjusted to half the value of the precedingsingle compression injection setting (as depicted by the width of thenarrower solid bars) to enable a symmetric double compression injection(although an asymmetric injection may alternately be performed). Thetiming of the two injections may also be adjusted so that the fuelamount delivered by the two injections is the same as that of thepreceding single compression injection setting. Further still, theduration of opening and closing of the fuel injector may be decreased(as depicted by narrower solid bars) and the timing in between the twoinjections may be increased.

The tenth example illustrates a quadruple compression injection insteadof the previous single compression injection. Herein, the amount of thefour injections is adjusted to a fourth of the value of the previoussingle compression injection setting (as depicted by the width of thenarrower solid bars) to enable a symmetric quadruple compressioninjection (although an asymmetric injection may alternately beperformed). The timing of the four injections may also be adjusted sothat the fuel amount delivered by the four injections is the same asthat of the initial single compression injection setting. Further still,the duration of opening and closing of the fuel injector may bedecreased (as depicted by narrower solid bars) and the timing in betweenthe four injections may be increased. It will be appreciated that in allthe depicted examples, the fuel injection may precede an ignition event.

In this way, by adjusting the split ratio of a fuel injection responsiveto the alcohol content of the fuel, improved evaporation and atomizationof the fuel may be enabled, and fuel losses at engine cold-start may bereduced. By enhancing the engines' ability to start with alcohol basedfuels at cold temperature conditions, the need for additional hardware,such as heated injectors, or additional steps, such as pilot fuelinjections, may be reduced. Additionally, the quality of cold-startexhaust emissions may be improved. By improving the mixing of air andfuel during combustion events, the efficiency of combustion may beimproved, leading to potential fuel economy benefits.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various steps,operations, or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedsteps or functions may be repeatedly performed depending on theparticular strategy being used. Further, the described steps maygraphically represent code to be programmed into the computer readablestorage medium in the engine control system.

It will be further appreciated that the configurations and routinesdisclosed herein are exemplary in nature, and that these specificembodiments are not to be considered in a limiting sense, becausenumerous variations are possible. For example, the above technology canbe applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types.The subject matter of the present disclosure includes all novel andnon-obvious combinations and sub-combinations of the various systems andconfigurations, and other features, functions, and/or propertiesdisclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. A method of operating an engine cylinder including a direct fuelinjector, comprising, during an engine cold start, direct injecting atleast some fuel in a compression stroke of the engine and at least somefuel in an intake stroke of the engine; and decreasing a ratio of intakestroke fuel to compression stroke fuel as an alcohol content of theinjected fuel increases; and transitioning to a single fuel injection.2. The method of claim 1 wherein decreasing a ratio of intake strokefuel to compression stroke fuel includes decreasing an amount of fuelinjected in the intake stroke while correspondingly increasing an amountof fuel injected in the compression stroke.
 3. The method of claim 2,wherein a sum of the amount of fuel injected in the intake stroke andthe amount of fuel injected in the compression stroke is based on anintake air charge, and wherein the sum increases as the alcohol contentof the injected fuel increases.
 4. The method of claim 1, whereindecreasing the ratio is performed for a first number of engine cylindersfor a second number of combustion events from a beginning of enginerotation, one or more of the first number and second number adjustedbased on the alcohol content of the injected fuel.
 5. The method ofclaim 1, further comprising, adjusting one or more of an ignition sparktiming and a fuel rail pressure based on the decreased ratio.
 6. Themethod of claim 5, wherein the adjustment includes retarding ignitionspark timing based on the decreased ratio.
 7. The method of claim 1,wherein an engine operating parameter is adjusted based on the decreasedratio.
 8. The method of claim 1, further comprising, maintaining a startof injection timing of the intake stroke fuel injection and maintainingan end of injection timing of the compression stroke fuel injectionwhile decreasing the ratio.
 9. The method of claim 2, furthercomprising, increasing a number of injections in the compression strokeif the amount of fuel injected in the compression stroke exceeds athreshold.
 10. The method of claim 1 wherein the transitioning to thesingle fuel injection includes transitioning to the single fuelinjection while adjusting turbocharger boost.
 11. A method of operatingan engine including an injector configured to directly inject fuel intoan engine cylinder, comprising: during a first engine cold start, directinjecting a first fuel in an intake stroke of the engine and acompression stroke of the engine at a first split ratio of intake strokefuel to compression stroke fuel; and during a second engine cold start,direct injecting a second fuel in the intake stroke of the engine andthe compression stroke of the engine at a second, lower split ratio ofintake stroke fuel to compression stroke fuel, the second fuel having ahigher alcohol content than the first fuel; and transitioning to asingle fuel injection while adjusting turbocharger boost.
 12. The methodof claim 11, wherein during the first engine cold start, the directinjection at the first split ratio is performed for a first number ofcombustion events from a beginning of engine rotation, and whereinduring the second engine cold start, the direct injection at the secondsplit ratio is performed for a second, higher, number of combustionevents from the beginning of engine rotation.
 13. The method of claim12, wherein during the first engine cold start, the direct injection atthe first split ratio is performed in a first number of enginecylinders, and wherein during the second engine cold start, the directinjection at the second split ratio is performed for a second, higher,number of engine cylinders.
 14. The method of claim 12, wherein duringthe first and second engine cold start, an ignition spark timing isadjusted based on the split ratio of the direct injection.
 15. Themethod of claim 14, wherein during the first engine cold start, directinjecting the first fuel in the intake stroke includes initiating directinjection in the intake stroke at a first timing, and direct injectingthe first fuel in the compression stroke includes terminating directinjection in the compression stroke at a second timing; and whereinduring the second engine cold start, direct injecting the second fuel inthe intake stroke includes initiating direct injection in the intakestroke at the first timing, and direct injecting the first fuel in thecompression stroke includes terminating direct injection in thecompression stroke at the second timing.
 16. A method of operating anengine cylinder including a direct fuel injector, comprising, during anengine cold start, direct injecting at least some fuel in a compressionstroke of the engine and at least some fuel in an intake stroke of theengine; and decreasing a ratio of intake stroke fuel to compressionstroke fuel as an alcohol content of the injected fuel increases; andtransitioning to a single fuel injection while adjusting spark timing.17. The method of claim 16 wherein decreasing a ratio of intake strokefuel to compression stroke fuel includes decreasing an amount of fuelinjected in the intake stroke while correspondingly increasing an amountof fuel injected in the compression stroke.
 18. The method of claim 16,wherein an engine operating parameter is adjusted based on the decreasedratio.